The present invention relates in general to verifying the proper interconnection of audio speakers in automotive audio systems, and, more specifically, to detecting a back-EMF as an indication of the proper interconnection of a speaker.
During manufacture of an automotive vehicle, it is necessary to test the interconnection between an audio system and its loudspeakers in order to ensure the quality of the finished vehicle. During manufacture, various wiring problems can be experienced including failure to properly join the harness wiring to the speaker terminals, bent or broken terminals, and pinched or broken wires in the harness. These problems need to be detected and then corrected before a finished vehicle leaves the factory.
Existing speaker detection methods include what is known as a speaker walk-around test, wherein the audio system is placed into a test mode in which it sequentially sends an output audio signal (e.g., the output from an AM/FM radio tuner) individually to each speaker while a person listens to determine if proper sound comes from each speaker. Due to the loud ambient noise level in a vehicle assembly plant, however, it is difficult for a listener to detect the absence of noise from a single speaker. Consequently, detection errors occur.
It is also known to employ each speaker as a generator (i.e., a pick-up or microphone) to generate a signal for sensing the presence of a properly connected speaker. By forcibly moving a speaker cone, a voltage is created across the speaker. But since a speaker is not optimized to perform as a pick-up, a high sound-pressure level has been required to generate a detectible signal. The prior art has used a door closing or door slam to provide a sound pressure impulse to the speaker cone. If a speaker is present, then the door slam generates a voltage detectable by the audio system to verify the presence of a speaker. However, this method is time consuming and is not reliable. The test requires certain test conditions such as a substantially airtight passenger cabin with all windows raised in order to ensure the desired movement of the speaker cone. The pressurization of the cabin caused by the door slam is not well controlled or repeatable, which means that the test results are highly variable and therefore difficult to classify. Furthermore, the prior art methods are not well adapted for detecting intermittent speaker connection problems after a vehicle is put into service since they require interaction by a human test operator.